Heat sealing machine



July 21, 1953 N. LANGER HEAT SEALING MACHINE Filed April 6, 1951 67 85 y f1 ya /rzllll/zllllllllll//lllllll INVENTOR.

Patented July 21, 195,3

prurito STATES PATENT OFFICE HEAT SEALING MACHINE Nicholas Langer, New York, N. Y.` Application April 6, 19'51, Serial No. 219,666

claims. (o1. 154-42) This invention relates to the art of heat sealing, and, more particularly, to a novel and improved machine and method of heat sealing thermoplastic sheet materials formed oi rubber hydrochloride, -viny1` resins, polyethylene, vinyledene chloride, and the like.

Present commercial heat sealing machines genhaving uniform thickness throughout the sealing region.v Considerable diiculties have been experienced, however, when it was desired to seal plies of such materials where th-e thickness of the plies or the number of the plies was diierent vin different portions of the sealing region. lThis situation arises, for example, when sealing across gusseted tubular stock or across gusseted bags of thermoplastic sheety material in which case the number of plies or layers to be sealed or bonded together may vary lbetween 2 and 4. Obviously, conventional heat sealing'equipment was unable to apply the uniform desired pressure where the eiiective thickness of the plies was subject to such extreme variations. In most cases, the applied pressure was excessive where the number of plies or their combined thickness was themaximum and insufficient for the production ofr a satisfactory seal Where the number of plies or their combined thickness was the minimum. This circumstance seriously interfered with the use of heat sealing in connection with gusseted bags and in general in the bonding of plies of thermoplastic sheet material of non-uniform thickness in the sealing region.

I have discovered that the outstanding problem may be solved in a remarkably simple manner.

It is an object of the present invention to improve heat sealing machines of the described general type.

It is another object of the present invention to provide a novel and improved machine and method for heat sealing thermoplastic sheet materials capable of forming seals or bonds of satisfactory quality regardless of variations in the thickness of the plies to be bonded in different portions of the heat sealing regions.

It is afurther object of the present invention to provide ay heat sealing machine, the pressure member of which comprises a pressure face constituted by a wall of an inflated or inflatable bag of elastic material adapted to readily conform to the surface contour of the plies of thermoplastic sheet material interposed between said pressure member and a sealing member. 'l

The invention also contemplates a heat sealing machine and method, particularly adapted to sealing practices in accordance with the thermal impulse principle disclosed and claimed inmy Patent No. ZAGGASO in which both the pressure, as Well as the heat, applied to the plies of thermoplastic sheet material may be caused to vary during each sealing cycle as predetermined and correlated functions of time.

Other and further objects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawing, in which Fig. 1 is a side elevational view, somewhat dia-` grammatic and fragmentary in character and having parts in section, of a heat sealing machine embodying the principles of the present invention;

Fig. 2 is a section taken on line 2-2 of Fig. l;

Fig. 3 is a View similar to Fig. 1, showingthe machine in its operative or heat sealing position;

Fig. 4 is a side elevational view, also somewhat diagrammatic in character and having parts in section, of av modified embodiment of the kinvention;

Fig. 5 is a similar view illustrating the machine of Fig. 4 in its operative condition; and

Fig. 6 is a diagrammatic view of a further modified embodiment of the invention.

Referring now more particularly to Figs. l and 2 of the drawing, reference numeral I il denotes a sealing member or bar, having an operative. or sealing face I I, adapted to be heated to or maintained at heat sealing temperatures; This may be accomplished, for example by forming the sealing member or bar IB of metal of high heat conductivity and providing in an inner cavity I2 thereof a suitable electrical heating element or cartridge I3.

The sealing member I is arranged for cooperation with a pressure member or bar I4, mounted on a reciprocable support I5. Pressure member or bar I Il may beformed of any suitable material having strength, such as steel or some other metal.

On the lower face of pressure member i4 is mounted a hollow tubular member It formed of elastic material, such as natural or synthetic rubber having an inner space ll therein. A material particularly suitable for the purposes of the present invention is a synthetic elastomer available in commerce under the name of silicone rubber due to the fact that this material is not affected adversely by the temperatures encountered in the operation of the machine. The lower exposed surface i8 of member i6 constitutes the operative or pressure-exerting face of the pressure member lll.

Great variations are possible in the character and shape of elastic member i6 in accordance with the specific sealing or bonding problem con-V templated. It may be, for example, in the form of a sealed pad or bag of relatively thin-walled elastic material. Thus, good results are obtained by forming the elastic member lE from a tube of silicone rubber of generally oval or somewhat liettened oval cross section which is cemented, clamped or otherwise secured to the lower face of pressure member or bar lli. The wall thickness of elastic member i6 is largely determined bythe strength of the elastic material and by the desired sealing pressure In general, the wall thickness is preferably the minimum that is compatible with the internal pressures thereby assuring maiiimum compliancy of the member.

A body of fluid is sealed in the inner space l? of elastic member i6. This may be a compressible fluid, such as air or some other gas, or a non-compressible fluid, such as water or oil.

It is also possible, however, to fill part of the said inner space with a non-compressible fluid and the remainder of said space with a compressible fluid.

To facilitate the introduction of the fluid into space Il, and the discharge of such fluid therefrom, if desired, it is preferred to mold a short metal tube I9 and 2li in the respective ends of the elastic member, valves 2| and 22 being respectively provided for the said tubes.

As the practical advantages obtainable by the present invention are particularly apparent when sealing plies of thermoplastic sheet material having different thicknesses in different portions of the sealing region, the operation of the machine will be described in connection with the sealing of a gusseted bag 23 of thermoplastic sheet material, comprising longitudinal seam 24 and gussets 25. It will be noted that in the compressed position of such bag, there will be four plies of the thermoplastic sheet material present in the regions of the gussets 25, three plies in the region of the longitudinal seam 24 and only two plies in the remainder of the sealing region.

The elastic member is assumed to be lled with a fluid, such as air, under suitable pressure through one or both tubes i9 and 20 and the inner space is then sealed by shutting olf the corresponding Valves 2l and 22. Of course, the same body of sealed-in fluid may be used indefinitely unless it is desired to change the fluid used or its internal pressure.

From the foregoing description, the operation of the heat sealing machine embodying the invention will be readily understood by those skilled in the art. Upon relative displacement of sealing member IB and pressure member f4 towards each other by any suitable reciprocating mechanism (not shown), bagV 23 will be compressed between sealing face Il of sealing member I0 and the pressure face of pressure member i4 constituted by the face of wall I8 of elastic member 4 or pad H3. As it will be noted by referring to Fig. 3, due to its flexible character, the face of elastic wall i8 will readily conform to the surface contour of compressed bag 23. In accordance with the elementary laws of hydrodynamics, the pressure applied to various portions of the sealing region will be substantially uniform, regardless of the number and the combined thickness of the plies in such portions. In other words, the applied pressure will be substantially the same in the regions of gussets 25, in the region of longitudinal seam 2li, and also in the remainder of the sealing region. In this manner, a highly satisfactory seal or bond of the several layers or plies will be produced by the combined action of sealing heat and uniform pressure.

Instead 0f maintaining a sealed body of compressible or non-compressible fluid within inner space l1 of elastic pad I6, it is also possible to continuously pass a iiow of such fluid under predetermined constant pressure through such space. rlhis mode of operation may be carried into practice by introducing the fluid through tube I9 and discharging such iiuid through tube 2Q, leaving, of course, both valves open to a greater or lesser extent, the pressure of the lluid and the extent to which the said valves are open determining the velocity of the flow. Maintaining a flow of suitable fluid, such as water, through inner space il of the pad will also produce a definite cooling eifect on the sealed region which is particularly beneficial when the sealing member lli is not continuously heated to heat sealing temperature but is of the thermal impulse type, such as is disclosed in my U. S. Patents 2,460,460 and 2,509,439. As most elastomers are relatively poor conductors of heat, small particles of material of good heat conductivity, such as metal powder may be incorporated into the elastic material of which the pad i6 is formed.

Figs. e and 5 illustrate a modified embodiment of the invention in which no separate reciprocating means are necessary for applying sealing pressure upon the plies of thermoplastic sheet material to be sealed or bonded together'. Reference numeral 33 denotes the sealing member having a sealing face El adapted to be heated to heat sealingr temperature in any suitable manner, such as by means of an electric heating cartridge 32. It is also possible, however, to employ a sealing member of the thermal impulse type, as disclosed and claimed in my aforesaid patents.

Pressure member 34 has cemented or otherwise secured to its lower face an iniateable pad 3S of elastic material, the lower wall surface 3S of which constitutes a yielding pressure-exerting face for the machine. Inner space 3l of pad 36 is in communication through a molded-in tube 40 and flexible hose il with nipple :l2 of a threeway valve 133. Inlet nipple lill of three-way valve i3 is connected to a suitable source of fluid under pressure through a control valve and outlet nipple S of the said three-way valve is in communication with the exterior through a similar control valve In the operation of the machine layers or plies 48 and #lil of thermoplastic sheet material are interposed between sealing face 3l and pressure face 38 of the machine. (Fig. Il.) Elastic pad 36 is in its deflated position, since in the illus- "trated position of the three-way valve 113, inner hose 4l, nipples 42 and 46 connected to each other by three-way valve 43 and. normally open control valve 41.

Three-way valve is now turned in the clockwise. direction by QGdegrees. (Fig. 5.) Fluid under pressure is now being introduced into elastic pad 36, through normally open control valve 45, inlet nipple d4, connected by the three-way valve'to nipple 42, hose 4I and tube 40. The elastic pad will beinflated and its lower face 38 will exert sealing pressure upon the thermoplastic plies 43 and 49. Sealing or bonding of the said plies will occur as a result of the combined action of heat and pressure eiective inthe sealing region.

Uponthe seal being completed, three-way valve '53 is turned counter-clockwise by 90 degrees, thusv being returned into its position illustrated in Fig. 4. This will cause the internal pressure in elastic pad S-being released into the atmosphere, causing deflation of the pad in agmanner well understood. The sealed plies Aof thermoplastic sheet material are then removed from the machine.

Obviously, the rate at which the iiuid pressure will be built up in pad 36 and is reduced is capable of adjustment in various ways, for example by adjusting the setting of valves 45 and 41. The fluid under `pressure necessary for the operation of the machine may be obtained from various sources, such as from a small compressor or from as well as to operate, due to the fact that the usual reciprocating mechanism, generally comprising an electric motor, a reduction gear, and a clutch, is completely dispensed with. However, it is also within the contemplation of the invention to combine a suitable reciprocating mechanism with members 30 and 34 whereby relative displacement of the said members with respect to each other is produced in addition to the rela- In the simplest tive displacement of sealing face 3l and pressurec exerting face 38 caused by inflation and deflation of elastic pad 36.

A further modied embodiment of the present invention which is particularly advantageous in combination with sealing members of the thermal impulse type is diagrammatically illustrated in Fig. 6,

Reference numeral generally denotes a sealing member of insulating material having a heater element 5l in the form of a strip or band of a metal of high speciiic resistance mounted thereon by means of bolts 52 and nuts 53. .The heater element constitutes the operative or sealing face of member 50. Through bolts and nuts 52, 53, the ends of heater element 5| are respectively connected to the ends of secondary or low-voltage winding 54 of a step-down transformer 55. The primary or high-voltage winding 56 is connected through a rheostat 56a and the normally open contacts 51 of a time delay switch 53 to a source'of 'alternating current of power line frequency indicated by terminals 59 and 66. The time delay switch 58 further comprises an actuating plunger 6l, depression of which initiates operation of the switch, and a control screw 62 for adjustment ofthe time delay period. vrlThis switch is of the type that, upon its operation being initiated, it will immediately close its operating contacts and will automatically open such contacts a predetermined kand adjustable time delay period thereafter. As time delay switches of the described general type are well known to those skilled in the ar-t and do not form part of the present invention, the switch has been merely diagrammatically indicated in the drawing. For structural details of suitable switches reference may be had, for example, to my Patent 2,479,375.

Pressure-member 63 is carried by ar reciprocable support 64. On the lower surface of the. pressure member there is mounted an inflatable'y pad 65 of elastic material having an inner space. V66 therein. The lower wall surface of the said pad constitutes a yielding pressure-exerting face 61 of the machine.

Pressure fluid may be introduced into the inlateable pad 65 and may be discharged there-- from under the control of a slide valve 68 comprising a stationary portion 69 and a movable portion or slide 19. Slide 10 is normally held against a projecting portion 1l of element 69 by a spring 12 and is capable of downward displacement upon solenoid 13 being energized,- which will then attract core 14 and will exert; a downward displacement on the slide through. pull rod 15 until the lower surface of the slide.- hits against stop 16.

The stationary portion 69 of slide valve 63 is provided with three ducts, 11, 18 and 19, passing therethrough. Of these, duct 11 is connected to a source of fluid under pressure (not shown) through a conduit B0 and adjustable valve 8l, duct 18 is connected to the inner space 66 of elastic pad l65 through two short metal conduits 82, 83 and an interposed flexible tube 84, and duct 19 is in communication with the external atmosphere through a conduit 85 and an adjustable valve 86. Slide portion 10 of slide valve 68 is provided with a'semicircular duct 81. It will be noted that in the upper or rest position of slide valve 68 (see Fig. 6), ducts 19 and 18 are connected with each other by means of semi-circular duct 81, whereas in the lower or operative position of the slide valve ducts 18 and 11 are connected with each other by means of the said semi-circular duct.

One end of solenoid 13 is directly connected to terminal 66 of the alternating current power line, while the other end of the said solenoid may be connected to the other terminal 59 of the power line upon actuation of the normally open contacts 68 of time delay switch 69, having an actuating plunger 99 and a control knob 9| which serves for adjustment of the time delay period. Time delay sw-tch 89 is of a. type similar In other words, it will.

to that of switch 58. close its contacts 88 upon depression of actuating plunger 90 and will automatically openthe said contacts a predetermined time delay period thereafter.

The actuating mechanism for the time delay switches comprises a horizontal bar Bla mounted on pressure member 63 from which depend two actuating rods 92 and 93, carrying adjustable screws 94 and 95, respectively, at their lower ends. Upon downward displacement of pressure 4nember 63, screws 94 and 95 will engage and then depress actuating plungers 6| and 90 of time delay switches 58 and 89, respectively, initiating the operation thereof.

From the foregoing description, the operation 7 of this modified embodiment of the invention will be readily understood. Plies or layers 95 and 96 of thermoplastic sheet material are introduced between pressure member 63 and sealing member 50 and the reciprocating mechanism is actuated, causing downward displacement of member 63 towards the other member. During this displacement screw 95 at the end of rod 93 will strike against plunger 90 of time delay switch 89.

The time delay switch will close its contacts 88, thus completing the energizing circuit of solenoid 13, which will exert a downward pull n core 14 and through pull-rod 15 will displace slide 16 into its lower or operating position against the biasing force of spring 12 until the lower face of the slide strikes against stop 16.

The inner space 66 of inflatable pad 65 is now connected to the source of iiuid pressure through conduit 82, flexible tube 84, conduit 83, ducts 18, 81 and 11, conduit 80 and valve 8l. Pad 65 will be iniiated at a predetermined rate, as determined by the extent to which valve 8i is opened and its yielding pressure-exerting face 61 will place plies 95 and 95 to be bonded together under pressure.

Sometime during downward displacement of pressure member 63, screw 94 at the lower end of actuating rod 92 will strike against actuating plunger l of time delay switch 58. Contacts 51 of the said switch will be closed, completing the circuit of primary winding 56 of transformer 55 with the power line 59, 60. Upon the transformer being energized, its secondary or low voltage winding 54 will energize heater element 5i of sealing member 50. Due to its extremely low heat capacity, the said heater element will be heated to heat sealing temperature practically instantaneously. As a result of the combined action of sealing heat and pressure, plies 85, SS will be bonded together.

A short predetermined period thereafter time delay switch 53 will automatically open its contacts 51, opening the circuit of transformer 55. The generation of heat in heater element 5i will be discontinued and the seal formed is permitted to cool and consolidate under pressure whereby a very strong and sound bond is obtained.

Another predetermined period thereafter, time delay switch 89 will automatically open its contacts 88, opening the circuit of solenoid 13. Slide 18 or slide Valve `5t will be returned into its rest position by spring 12. The inner space 6G of inflated pad 55 is now connected to the external atmosphere through conduit 82, iiexible tube 85:-, conduit 83, ducts 18, 81, 19, conduit 85 and control valve 85. The pad '65 will be deflated at a rate which is adjustable by the setting of control Valve 8E. This will remove the pressure from the sealed layers. Finally, pressure member 63 is displaced upwardly by the reciprocating mechanism thereby resetting the machine for the next bonding operation.

In the foregoing, a preferred procedure for operating the machine has been described. It is to be observed, that the machine of the invention is extremely flexible in its operation and may be preset for carrying out a great variety of sealing operations of different type. This is due to the fact that both the heating of the sealing face 5i, as well as the pressure applied by the pressure-exerting face 61 are individually adjustable as independent functions of time during each sealing cycle. This provides great advantages when sealing thermoplastic plies of different composition and thickness.

The time when pressure application is started is adjustable by screw 94, the length of time for which pressure is applied is adjustable by control knob 91. The rates at which the pressure is increased and decreased are adjustable by valves 8l and 86, respectively.

The time when heat application is started is adjustable by screw 94, the length for which heat is applied is adjustable by control knob 62. The amount of heat generated during the unit of time is adjustable by the setting of rheostat 56a. In general, it is preferred to have the period of pressure application extend beyond the period of heat application so that the seal formed is being cooled and consolidated while still under pressure.

In Fig. 6 a simplined form of sealing member of the thermal impulse type has been shown for the sake of simplicity. Further improved results may be obtained by using the sealing members of the thermal impulse type disclosed and claimed in my Patent No. 2,509,439 and in my co-pending application Serial No. 174,074, led July l5, 1950, now Patent No. 2,574,095.

While there has been shown and described what is at present considered to be the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various modifications and substitutions of equivalents may be made without departing from the teachings of the invention.

I claim:

l. A heat sealing machine comprising, in combination, a stationary sealing member having a sealing face adapted to be heated to heat sealing temperatures, and a pressure member therefor, said pressure member including an innatable pad of elastic material having a surface mounted on a stationary support and another surface constituting a yielding pressure-exerting face whereby upon iniiation of said pad uniform sealing pressure may be applied upon plies of thermoplastic sheet material interposed between said sealing face and said pressure-exerting race.

2. A heat sealing machine comprising, in combination, a stationary sealing member, a pressure member therefor' including an inflatable pad of elastic material having a surface mounted on a stationary support and another surface constituting a yielding pressure-exerting face, means for heating the operative face of said sealing member to heat sealing temperatures, and means for inflating said pad thereby applying uniform sealing pressure upon plies of thermoplastic sheet material interposed between said sealing face and said pressure-exerting face.

3. A heat sealing machine comprising, in combination, a stationary sealing member including a sealing face adapted to be heated to heat sealing temperatures, a pressure member therefor including a yielding pressure-exerting face constituted by a surface of an iniiatable pad of elastic material having another surface mounted on a stationary support, means for introducing fluid under pressure into said pad thereby to innate the pad and to apply sealing pressure upon plies of thermoplastic sheet material interposed between said sealing face and said pressure-exerting face, and means for discharging said fluid from said pad thereby to release said sealing pressure.

4. A heat sealing machine comprising, in combination, a stationary sealing member including a sealing face adapted to be heated to heat sealing temperatures, a pressure member therefor including a yielding pressure-exerting face constituted 'by a surface of an inflatable pad of elastic material, a stationary support for mounting the opposed surface of said pad, Valve means for introducing fluid under pressure into said pad thereby to iniiate the pad into pressure- 'applying relation with said sealing face and to discharge such fluid from the pad thereby to release the applied pressure, and means for controlling the pressure of said fluid.

5. A heat sealing machine comprising, in combination, a stationary sealing member including a sealing face adapted to be heated to heat sealing temperatures, a pressure member therefor including a yielding pressure-exerting face constituted by a surface of an inflatable pad of elastic material, a stationary support for mounting the opposed surface of said pad, means for introducing .fluid under pressure into said pad 10 thereby to inflate said pad into pressure-applying relation with said sealing face and to discharge such iiuid fro-m the pad thereby to release the applied pressure, and means for controlling the pressure of said fluid prevailing Within said pad as a predetermined function of time.

NICHOLAS LANGER.

References Cited in the file of this patent UNITED STATES PATENTS Number Nam-e Y Date 2,018,736 Norris Oct. 29, 1935 2,108,859 Kamborian Feb. 22, 1938 2,460,460 Langer Feb. 1, 1949 2,509,439 Langer May 30, 1950 2,520,978 Super Sept. 5, 1950 2,524,932 Schulman Oct. 10, 1950 2,550,006 Dreyfus Apr. 24, 1951 2,574,094 Ferrer et al. Nov. 6, 1951 

